Estimation of spin states of cobalt ions in LaCoO[formula omitted] nanoparticles by means of soft X-ray absorption spectroscopy

Abstract

Spin states of Co3+ ions in LaCoO3 nanoparticles of 20, 25 and 28 nm in sizes were studied by means of soft X-ray absorption spectroscopy at the O K and Co L2,3 edges. Using measurements of oxygen K X-ray absorption spectra, there were estimated the relative numbers of t2g and eg holes in hybridized vacant O 2p–Co 3d states. Based on the results of these studies, the relative amounts of low-spin and high-spin Co3+ ions were estimated. In particular, for LaCoO3 with an average nanoparticle size of 25 nm, approximately 60% and 40% of the Co3+ ions are in the low-spin and high-spin states, respectively. It corresponds to an effective spin Seff=0.8. A slightly different result was obtained using Co L X-ray spectra and multiplet calculations of the spectra of Co3+ ions. According to these data, about 2/3 of trivalent cobalt ions in the specimen with an average nanoparticle size of 25 nm are in the low-spin state. The results of measurements of X-ray absorption spectra can be explained quite well from the assumption that Co3+ electrons are in the mixture of low- and high-spin states.